Traveling-wave tube having a slow-wave structure of the cloverleaf type wherein the height of the cloverleaf sections are tapered



March 19, 1968 J,A RUETZ l-:TAL

l 3,374,390 TRAVELING-WAVE TUBE HAVING A SLOW-WAVE STRUCTURE OF' THE CLOVERLEAF TYPE WHERE'IN THE HEIGHT OF THE CLOVERLEAF SECTIONS ARE TAPERED 5 Sheets-Sheet l Filed March 29. 1965 WN .WN

March 19, 1968 1. A. RuETz ET AL 3,374,390

TRAVELING-WAVE TUBE HAVING A SLOW-WAVE STRUCTURE OF THE CLOVERLEAF TYPE WHEREIN THE HEIGHT OF' THE CLOVERLEAF SECTIONS ARE TAPERED Filed March 29, 1965 5 Sheets-Sheet 2 March 19, 1968 Y J. A. RUETZ ET AL v 3,374,390

TRAVELING-WAVE TUBE HAVING A SLOW-WAVE STRUCTURE OF' THE CLOVERLEAF TYPE WHEREIN THE HEIGHT OF THE CLOVERLEAF SECTIONS ARE TAPERED Filed March 29, 1965 5 Sheets-Sheet '5 March 19, 1968 1 A- RUETZ ET AL 3,374,390

TRAVELING-WAVE TUBE HAVING A SLOW-WAVE STRUCTURE OF THE cEovEEEEAE TYPE wHERETN TEE HEIGHT @E THE cLovERLEAT SECTIONS AEE TAPERED Faxe M Po ers ATTOR NEY March 19 1968 J. A. RUETZ ET AL 3,374,390

TRAVEEING-WAVE TUBE HAVING A SLOW-WAVE STRUCTURE 0E THE CLOVERLEAF TYPE 'WHERETN THE HEIGHT 0F THE CLOVERLEAF SECTIONS ARE TAPERED Filed March 29, 1965 5 Sheets-Sheet 5 "SATURVATEQ GAIN (db.)

FIG. IO

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ATTORNEY United States Patent() 3,374,390 TRAVELlNG-WAVE TUBE HAVING A SLOW- WAVE STRUCTURE F THE CLOVERLEAF TYPE WHEREIN THE HEIGHT 0F THE CLOVERLEAF SECTIONS ARE TAIERED John A. Ruetz, Los Altos, Willis H. Yocorn, Chatham, and Ren M. Rogers, Sunnyvale, Calif., assignors to Varian Associates, Palo Alto, Calif., a corporation of 'California Continuation-impart of application Ser. No. 56,415, Sept. 16, 1960. This application Mar. 29, 1965, Ser. No. 443,612

18 Claims. (Cl. S15-3.6)

This application is a continuation-in-part of copending patent application Ser. No. 56,415, filed Sept. 16, 1960, now abandoned.

This invention relates in general to electron discharge devices and, more specically, to a novel traveling wave tube amplifier suitable for providing megawatts of pulsed power output, and to a hybrid amplifier that utilizes a stagger tuned klystron buncher section followed by a traveling wave tube section.

Velocity modulation type beam tubes of the klystron type have been popularly used in recent years for the amplification of microwave frequencies, such klystron devices providing high gain and efficiency, high power and, in addition, a relatively wide bandwidth. For example, one klystron amplifier providing about 2 megawatt-s of peak power with a bandwidth of about 150 megacycles at an operating frequency of about 2.9 kmc. is presently in use. Velocity modulation electron discharge devices of the traveling wave tube type possess the ability to provide greater bandwidth than is possible with klystron tubes; however, the power h-andling capabilities of such traveling wave tube amplifiers have not 4been as good as those of the klystrons.

In one embodiment of the invention, a -traveling wave tube amplifier possesses a power handling ability comparing favorably to that of such klystron power amplifiers and which also provides the broadband characteristics typical of traveling wave tubes, for example, a power bandwidth approximately twice that of such power klystrons, that is, 350 me'gacycles. The traveling wave tube amplifier of the present invention, in addition to providing high power and wide bandwidth, also has the characteristics of high efficiency and high gain along with long life.

In another embodiment of the present invention a hybrid microwave amplifier tube is provided which includes a multi-cavity stagger tuned klystron driver section followed 'by a ybroadband traveling wave tube section. The multi-cavity stagger tuned driver section has a gain characteristic with gain deviations over the band supplementing the gain deviation of the traveling wave tube section such that the composite gain characteristic for the entire tube is quite uniform over a relatively wide band of frequencies. For example, 'the gain characteristic is at to 1 db over :|:6% frequency deviation from the center frequency of the passband of the tube. In a preferred ernbodiment the gain passband of the stagger tuned driver section is broader than the gain passband of the traveling wave tube section and the cavities of the driver section are tuned and loaded in such a manner as to peak up the driver gain response at the band edges. This novel tube also has greatly enhanced and unexpected maximum efliciency of 48%.

It is therefore an object of the present invention to provide a novel traveling wave tube structure for utilization as a broadband, high gain amplifier designed to provide kilowatts of average RF power output and megawatts of peak pulse power output.

It is another object of the invention to provide a microwave amplifier tube having uniform gain characteristics 3,374,390 Patented Mar. 19, 1968 with high efficiency over a relatively wide band of frequencies.

One feature of the present invention is the provision of a traveling wave tube amplifier possessing a novel output section which enables its utilization as a high power, broad bandwidth, long life amplifier of microwave frequencies.

Another feature of the pre-sent invention is the provision of a novel traveling wave tube amplier wherein improved transducers are employed, one for introducing the microwave frequency signal which is to be amplified into the input section of the traveling wave tube and a second transducer for coupling the output section of the traveling wave tube amplifier with an output load circuit, resulting in 'broadband operation.

Another feature of the present invention is the provision of a novel traveling wave tube amplifier of the above featured type which employs a slow Wave structure of the cloverleaf type.

Another feature of the present invention is the provision of a hybrid tube apparatus comprising a stagger -tuned klystron driver section followed by a traveling wave tube section, the gain characteristics of the klystron section being supplementary to the gain characteristics of the traveling Wave tube section, whereby the total gain characteristics of the tube are made more uniform than that of the traveling wave tube section alone over the passband of the tube.

Another feature of the present invention is the same as the preceding feature wherein the traveling wave tube section is a negative mutually inductive coupled slow wave circuit having a forward wave fundamental space harmonic mode of operation with the beam whereby uniform gain characteristics are achieved at relatively high efiiciencies.

These and other features and advantages of the present invention will become more apparent upon a perusal of the following specification taken in connection with the accompanying drawings wherein:

FIG. 1 is a longitudinal cross-section view of a traveling wave tube amplifier which embodies the present invention, the figure being broken and offset due to the length of the tube;

FIG. 2 is an enlarged cross-sectional view of a portion of the output end of the tube;

FIG. 3 is a transverse cross-sectional View of one of the slow wave sections of the amplifie-r taken along section line-s 3-3 in FIG. 2;

FIG. 4 is "a transverse cross-sectional view taken along section line 4-4 of FIG. 2 which discloses the output transducer utilized to couple the output power from the output section of the traveling wave Itube amplifier to the load circuit;

FIG. 5 is a transverse cross-sectional view taken along section lines 5 5 in FIG. 2;

FIG. 6 is a cross-sectional view taken along section line 6 6 in FIG. 5 looking in the output transducer;

FIG. 7 Iis a transverse cross-sec-tional view of the input transducer portion of the traveling wave tube in FIG. 1, this transducer having the form of .a coaxial line coupling;

FIG. 8 is a plot of curves showing the eiciency of tubes having various tapered ends in their slow wave structure;

FIG. 9 :is a longitudinal cross-sectional View partly in elevation -of a hybrid amplifier tube apparatus employing features of the present invent-ion; and

FIG. l0 is a graph of gain deviation versus frequency devi-ation showing the gain characteristics of the hybrid 0 tube :apparatus of the presen-t invention as compared with gain characteristics of the prior art.

Referring now to FIGS. 1-7, a ytraveling wave tube amplifier comprises a cathode gun assembly 11 including a mounting cylinder 12 secured to an annular pole piece 13 and to a cylindrical insulator 14 `as of ceramic. The other end of insulator cylinder 14 is vacuum sealed to an annular member 15, which in turn is vacuum scaled to the housing of the electron gun subassembly 16, thus longitudinally aligning the electron gun with res ect to the traveling wave tube slow wave structure. A tubular cathode socket 17 is secured to the member 15 and is adapted to receive a high negative beam pulsing voltage which -is applied by way of the member 15 to the electron gun housing 16 and by way of an internal lead (not shown) Ito one side of the heater filament (not shown) of the electron gun assembly. The electron gun assembly includes a metallic heater socket 18, a concave cathode emitter button 19, and annular focusing members 21.

The main body of the traveling wave tube amplifier, including the slow wave circuit, comprises annular support member 22, end plate 22 and .a cylindrical shaped anode 23, the anode 23 and plate 22 being provided with a central opening through which the electron beam from the cathode button 19 may enter the slow wave circuit. The input transducer 24 for this traveling wave tube amplitier, by means of which the signal to be amplified is introduced into the tube, is mounted therein and will be described more fully below.

The slow wave structure of this device comprises a plurality of circular periodic Sections of cloverleaf -configuration one of which is shown in detail in FIGS. 2 and 3, positioned in hollow cylindrical shells 25. The cloverleaf sections each include two metallic end walls 26 common to adjacent sections, each end wall having a circular beam opening 27 axially positioned therein, which also serves as a capacitive coupling opening lbetween sections. A sinuous or four element cloverleaf shaped metallic side wall 2S is brazed between the two end walls 26 of each section. `The common walls 26 separating the cavity sections are provided with a plurality of radially disposed inductive coupling slots 29 spaced apart every 45 relative to each other such that every other section is in alignment. The particular type of slow wave sections utilized in this traveling wave tube amplitier is described in U.S. patent application Serial No. 536,597 entitled Inductive Coupling Means and Methods for High Frequency Apparatus," filed September 26, 1955, by Marvin Chodorow, now abandoned and replaced by continuation application Serial No. 7,481 led February 8, 1960, now U.S. Patent 3,233,139, issued February 1, 1966. The coupling between these slow wave sections is `termed negative mutual inductive coupling, which gives the slow-wave structure a forward wave fundamental, and it is therefore a higher impedance structure than other types of slow wave structures. The higher impedance permits the attainment of a high efficiency for this traveling wave tube amplifier.

The slow wave structure is divided at approximately :the center of the tube by an attenuator section which comprises a pair of annular plates 31 secured together, each plate forming aside surface for a .cloverleaf section. The plates are also secured t-o the metal sleeves as by the Heliarc process. The plates are provided with attenuators in the form of spaced, carbon loaded ceramic discs 32 brazed to the plates in the four noses or cloverleafs of the center cloverleaf section, one set of discs terminating the front or input slow wave section and the other set of four discs providing a matched termination for the reflections set up on the output end of the tube in a manner known in the art. The periphery of the plates are provided with cooling channels through which cooling fluids may be passed for cooling the center section of the tube.

The right hand end of the output section shell 25 is secured to an annular plate 33 which forms a portion of the output transducer section of this traveling wave tube. It is noted that the last cloverleaf section of the slow wave structure is approximately half the height of the normal cloverleaf sections, the several cloverleaf sections preceding the last also varying progressively in height as explained below. The last clovrleaf section is coupled through the central opening 27 to an output waveguide 34 formed in the plate 33. A more detailed discussion of the construction of the output transducer will be found below.

The waveguide 34 formed in the plate 33 is coupled to output waveguide section 35 leading to a vacuum sealed window 36 adapted to be coupled to the output load circuit. A fluid cooled shielded electron beam collector is mounted on the end of the traveling wave tube, this co1- lector including the electron beam collecting member 27 and a pair of cylindrical jackets 38 and 39 surrounding the collector 37 and forming therebetween passages for the transmission of a cooling liquid around the collector. The collector 37 is insulatingly mounted on the main tube body by means of cylinder 41 and insulator ring 42. A hollow cylindrical X-ray shield having an outer steel shell 43 is also secured over the collector and collector cooling apparatus. An annular metallic pole piece 44 is also securely aixcd to the plate 33 of the traveling wave tube and provides the means, along with member 13, of connecting a focusing magnet to the tube to produce a beam focusing magnetic field extending along the entire length of the traveling wave tube in a well known manner. A getter type vacuum pump 40 is appended to the tube.

The input transducer 24 which supplies the radio frequency signal to the input end of this amplier tube includes a coaxial type connection 4S which extends radially into the tube through a cylindrical opening in the anode plate 22 and then bends 90 and extends longitudinally across the rst slow wave cloverleaf section by way of a longitudinal opening 46 in the cylindrical anode 23, the end of the connector 45 being secured to the far wall of the first section. The coaxial coupling member comprises the outer conductor 47 which is screwed into the jacket 48 and the inner conductor 45 which is insulated from the outer conductor by insulating cylinder 49. An annular stub 49 is secured in the end plate 22' and extends into the first slow wave cloverleaf section for capacitive tuning of the input section to thus aid in matching the longitudinally extending inner end of the coaxial input line to the cloverleaf input section.

The output section of this traveling wave tube is` arranged so that the height, that is, the distance between the end walls 26 of a cavity section taken along the longitudinal or beam axis, of the last several slow wave sections decreases progressively from the normal or full height of the initial slow wave sections. The height of the last cloverleaf section 51 is one-half the height of the full height sections, the section 52 preceding the last section has a height 5/s the normal height, the second section 53 preceding the last section has a height 1% the normal height, while the third section 54 preceding the last section is 7/ of the full height. The last or one-half height section is coupled to the reduced height waveguide 34 which is shorted at the end 34' (approximately VM from thc center of the beam) and which is tuned capacitively with the annular stub 55 penetrating into the waveguide from thc plate 33. The stub is threaded into the plate 33 and the spacing between the end plate or waveguide wall 26 and the stub may be varied during initial manufacture for proper capacitive tuning. The waveguide wall 26 has a one-half wavelength diameter hole 27 through which the energy from the slow wave structure is coupled into the output waveguide 34. The capacitive stub 55 is concentric with this hole and also passes the beam to the collector 37. The reduced height portion of the waveguide 34 is approximately 1/zk long and broadens in two steps into the final output waveguide section 35.

The novel structural features utilized in this traveling wave tube, particularly the output section of the tube including the output transducer, result in a power tube of exceptionally high etliciency as compared with similar type prior art traveling wave tubes. More specifically,

the change in the slow wave circuit phase velocity brought about by the gradual shortening of the height of the last several cloverleaf sections of this tube results in a tube with greatly enhanced eiiiciency. The particular reduction in height of the end sections shown, i.e., 7i, '3%1, Ss, 1/2 full height, is utilized for illustration purposes since other particular height reduction combinations may be utilized depending on the end results desired. The chart in FIG. 8 shows the efciency curves for a number of cloverleaf slow Wave structures with various reduced section combinations. Curve A is for a slow wave structure in which the heights of all the cloverleaf sections are constant. Curve B is a slow wave structure in which the last cloverleaf section is 1/2 normal height, the other sections all being of normal height. Curves C and D are for slow wave sections having two and three reduced height sections, respectively, while Curve E is for the particular reduced height structure shown in FIGS. l and 2. A selected height reduction of the end sections, resulting in a change in phase velocity, produces more optimum adjustment between beam and slow wave circuit wave before any appreciable energy is removed from the beam. Eiciency is also improved due to better synchronisrn as energy is removed from the beam.

In operation, the electron beam emitted from the cathode button 19 is focused by magnetic means (not shown) coupled to the pole pieces 13, 44 and passes through the openings 27 in the slow wave structure, the beam being finally collected in collector 37. The signal to be amplified is coupled into the first section of the slow wave structure through input transducer 24, the signal passing along the slow wave structure where it interacts in Well known manner with the electron |beam -to amplify the signal. The signal output is taken from the last slow wave section through the wavegui-de 35.

One traveling wave amplifier tube made in accordance with this invention had a frequency range of approximately 2.6 to 2.95 kilomegacycles, a peak power maximum of about 4.00 megawatts and minimum of about 2.0 megawatts, an average power of about 8.9 lrilowatts, and a bandwidth (3 db down in saturated power output) of approximately 14%. These specifications far exceed the results heretofore obtained with tubes of this type.

With reference to FIG. 9, there is shown iu longitudinal cross-section a hybrid tube apparatus incorporating the present invention. Such a hybrid tube apparatus is desc-ribed in detail in copending patent application Ser. No. 334,496, filed Dec. 30, 1963, now U.S. Patent 3,289,032, issued Nov. 29, 1966, and assigned to the same assignee. The tube includes a conventional electron gun assembly 101, as described in U.S.l Patent 2,944,187, issued July 5, 1960, inventor R. L. Walter et al. The electrongun serves to form and project a stream of electrons over an elongated beam path 102 directed axially of the tube. A collector assembly 103 is disposed at the opposite end of the beam path 102 for terminating the beam and for dissipating the energy thereof. The collector is of the conventional design described in US. Patent 3,054,925, issued Sept. 19, 1962, inventor R. L. Walter et al., and includes an X-ray shield 102 for shielding operating personnel from the X-rays generated within the collector 103.v A main body section 105 is disposed between the electron gun 101 and the collector 103.

The main body section 105 includes an anode electrode 106 for accelerating the electrons drawn from the electron gun 101 to beam voltage in the order of 120-140 kv.

The main tube body 105 includes a klystron buncher section 115 followed by a traveling wave tube section 116.

The klystron buncher section 115 includes a plurality of reentrant cavity resonators 117, 118, 119 and 120 successively arranged along the beam path in the conventional klystron manner. The traveling wave tube section 116 includes 13 successive sections 121 of a conventional cloverleaf slow wave circuit of the type described in the aforementioned U.S. Patent, 3,233,139. The cloverleaf traveling wave turbe section provides a fundamental forward wave space harmonic for operation with the electron beam as hunched by the klystron driver section to produce amplification of signal energy put on the beam by the klystron driver over a relatively wide band of frequencies.

The gain characteristic of the multicavity stagger tuned klystron driver section 115 is arranged such that it supplements the gain characteristic of the traveling wave tube section 116. In a preferred embodiment of the present invention the traveling wave tube section 116 is a negative mutually inductively coupled circuit, such as for example, a cloverleaf section as shown in FIG. 9 and has a gain characteristic as shown in FIG. 10 by curve 125. More specifically it can be seen that the small signal gain characteristic of the cloverleaf section begins to rapidly fall olf for a frequency deviation out from the center frequency of the band greater than 2%. Thus if one is to obtain uniform gain characteristic over a wider band of frequencies the gain in the band edges must be increased. Accordingly, the small signal gain characteristic of the multicavity driver section 115 is shown as line 126 in FIG. 10 and is arranged to supplement the gain of the traveling wave tube section 116.

The cavities 117-120 are tuned to frequencies as indicated by the arrows at the lbottom of the graph and are heavily loaded, preferably by beam loading, to loaded Qs as indicated less than 200 and coupled to the beam with coupling coeiiicients of M=0.8 as indicated to provide supplementary gain deviation at the band edges of the gain characteristic 126 of the traveling Wave tube section 116. The gain characteristic curves 125 and 126 for the m-ulticavity driver section and the traveling wave tube section 115 and 116, respectively, are the small signal gain characteristics which are more susceptible to calculation than are the large signal gain characteristics which latter characteristic more truly represent the gain characteristics of the tube under normal operating conditions. However, the small signal gain characteristics are generally indicative of the large signal gain characteristics except that the large signal gain characteristics have less pronounced deviations from a norm, suc-h as the average, than the small gain characteristics. In other words, a large signal characteristic can be approximated by rounding and tending to level out the humps and dips in the small signal gain characteristic curve.

The total large signal gain characteristic of the hybrid tube apparatus of FIG. 9 is shown as line 127 of FIG. l0. This total gain characteristic for the tube shows that the gain response is substantially uniform over a band of 10% at the operating frequency of the tube. This uniform gain characteristic 127 represents a major improvement in broadband amplier tubes because it permits constant drive power over the band to produce uniform maximum power output at relatively high efficiency. Heretofore, in order to achieve even less bandwidth it was necessary to increase the signal power at the band edges by as much as 5 to 10 db but with the present hybrid tube the input signal generator, now shown, can be simplified as it need only provide constant power output over the operating band of the tube which is quite easily achieved at the low power levels, i.e., watts to hundreds of watts required to drive the klystron section 115.

In operation, a beam is formed in the electron gun 101 and projected longitudinally of the tube through the anode 106, klystron driver section 115, traveling wave tube section 116 and collected in the collector 103. Signal energy to be amplified is fed into the first cavity 116 via a coaxial input line 141 and input loop 142. The signal energy applied to cavity 116 velocity modulates the beam which is transformed into current density modulation of the beam after passage through the iirst drift tube section 143. Successive cavities 118, 119 and 120 serve to further velocity modulate the beam in the conventional klystron manner to amplify the current density modulation of the beam after passage through the successive drift tube sections 144. After leaving the last drift tube section 144 the current density modulated beam with the signal energy impressed thereon enters the input end of the traveling wave tube section. In a preferred embodiment the distance L from the center of the gap of the last driver cavity 120 to the center of the first cloverleaf section 121 is made as short as possible, however, the operating data for the tube of FIG. 9 was obtained with an L=38 degrees of reduced plasma wavelength of the beam.

The current density modulated beam excites a signal on the slow wave circuit 116. The signal on the circuit moves in the forward direction in synchronism with the current density modulation of the electron beam to produce a growing wave on the slow wave circuit 116. The signal is extracted from the slow wave circuit 116 at the terminal end thereof and fed via waveguide impedance transformer section 145 and flared waveguide section 146 to an output window assembly 147. The output window assembly 147 includes a wave permeable window member 48 as of alumina ceramic sealed across the output waveguide section in a vacuum tight manner to permit passage of the wave energy therethrough while maintaining a vacuum in the tube apparatus. The output window is of the conventional design as described in U.S. Patent 2,958,834, issued November l, 1960, inventor Robert S. Symons et al. After passage through the window assembly 147 the wave energy is propagated to a load, not shown.

An RF termination section 150 is provided at the input end of the traveling wave tube section 116 for dissipating wave energy on the traveling wave tube circuit traveling in the backward direction such wave energy often being produced by reflections at the terminal end of the traveling wave tube section 116. The terminating section 150 is a half height section of the cloverleaf structure provided with lossy dielectric members 151 disposed on the noses of the inwardly directed side wall projections of the cloverleaf circuit. The lossy terminating section 50 is capable of dissipating 500 watts average power to prevent undesired oscillation in the output traveling wave tube section 116.

Further detail structure of the main tube body 105 is that the anode 106 includes an outer annular ring member 161 as of copper sealed at its periphery as by brazing to an envelope segment 162 as of iron of the electron gun 101. Sealed within the central interior of the ring member 161 is a flared throat member in axial alignment with the beam path to converge the beam drawn from the gun therethrough. Throat member 163 as of copper is provided with an annular hollow passage 164 therein for the passage of coolant therethrough for cooling of the anode 106 in use.

A magnetic cathode pole piece 172 surrounds the anode and is provided with a magnetic adaptor ring 173 serving as one pole piece of a magnetic beam focusing solenoid 186. The adaptor ring 173 is fixedly secured to the magnetic pole piece 172 as by screws, not shown.

A collector pole piece 174 is provided at the collector end of the main tube body 105 and similarly forrns the collector pole piece of the beam focus solenoid. The collector pole piece is centrally apertured for the passage of the beam therethrough and serves to collect the beam focusing magnetic eld after its passage from the anode pole piece through the main tube body to the collector pole piece 174 and to return the magnetic flux to the solenoid 186.

The klystron driver section 115 is strengthened by the provision of four longitudinally directed quadraturely spaced rods 175 as of nonmagnetic stainless steel connected at one end to the anode pole piece 172 and connected at the other end to a plate 176 as of stainless steel affixed to the upstream end of the slow wave section 116. A plurality of transverse plates 177 as of stainless steel 8 interconnect the rods and the drift tube members 143 and 144 to provide rigidity to the klystron buncher structure 115.

A copper plate 173 surrounds the lossy load terminating cloverleaf section S0 of the traveling wave tube section 116 for carrying the heat away from the load. A cooling pipe 181 surrounds the plate and coolant is circulated through the pipe 181 for carrying away the heat. A stainless steel tube 182 is vacuum sealed at one end to the plate 78 and forms the vacuum envelope for the slow wave circuit section 116. The tube 182 is sealed at the other end to a similar end plate 183 as of copper. The end plate 183 has the output terminal for the slow wave circuit 116 and the transformer 145 formed therein. A getter-ion vacuum pump 184 is disposed in gas communication via tubulation 185 with the interior of the tube for maintaining a low vacuum pressure as of 109 mm. Hg within the vacuum envelope of the tube.

Since many changes can be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. An electron discharge device comprising: a cathode for producing a beam of electrons, a collector for collecting said beam of electrons, a slow-wave structure positioned between the cathode and collector for supporting a traveling wave, input means coupled to the cathode end of said slow-wave structure for introducing the traveling wave onto the slow-wave structure, the traveling wave being amplified by interaction with the electron beam traveling through the slow-wave structure, said slow-wave structure comprising a plurality of inductively coupled cloverleaf sections aligned along the beam path, the heights of the last several cloverleaf sections in the slowwave structure decreasing in value progressively7 the last cloverleaf section being substantially shorter in height then the full height of the normal cloverleaf sections, said input means including a coaxial line extending into and across the first cloverleaf section in a direction parallel to the beam path, said first cloverleaf section having an annular tuning stub coaxially aligned with the beam path and extending into said first cloverleaf section for capacitive tuning of the input, and output means coupled to said last cloverleaf section for removing the wave energy from said slow-wave structure.

2. An electron discharge device as claimed in claim 1 wherein said output means comprises a waveguide positioned between said last cloverleaf section and said collector means.

3. An electron discharge device as claimed in claim 2 wherein said waveguide is coupled to said last cloverleaf section through a coupling hole in a wall separating the last section yfrom the output waveguide, said coupling hole being coaxially aligned with the beam path through said slow-wave structure.

4. An electron discharge device as claimed in claim 3 wherein said coupling hole has an approximate onehalf wevelength diameter.

5. An electron discharge device as claimed in claim 3 wherein said output waveguide has an annular capacitive tuning stub extending therein and aligned with the beam path and coupling hole for tuning the circuit.

6. An electron discharge device comprising: a cathode for producing a beam of electrons; a collector for collecting said beam of electrons, a slow-wave structure positioned between the cathode and collector for supporting a traveling wave, input means coupled to the cathode end of said slow-wave structure for introducing the traveling wave onto the slow-wave structure, the traveling wave being amplified by interaction with the electron beam traveling through the Slow-Wave structure, said slow-wave structure comprising a plurality of inductively coupled cloverleaf:` sections aligned along the beam path, the heights of the last several cloverleaf sections in the slowwave structure decreasing in value progressively, the last cloverleaf section being substantially shorter in height than the full height of the normal cloverleaf sections, and a waveguide output coupled to said last cloverleaf section -for removing the amplified -wave from the slowwave structure, said input means including a coaxial line, the center conductor extending across the first cloverleaf section parallel to the beam path through the cloverleaf section, and an annular capacitive tuning stub extending into the first cloverleaf section parallel with the center conductor and aligned with the beam path for tuning the input.

7. An electron discharge device as claimed in claim 6 wherein said output waveguide is positioned between said last cloverleaf section and said collector, said output waveguide being coupled to said last section through a coupling hole in a wall separating said last section from said output waveguide, said coupling hole being coaxially aligned with the beam path through said slowwave structure.

8. An electron discharge device as claimed in claim 7 -wherein said coupling hole has an approximate onehalf wavelength diameter.

9. An electron discharge device as claimed in claim 7 wherein said output waveguide has an annular capacitive tuning stub extending therein and aligned with the beam path and coupling hole for tuning the output.

10. An electron discharge device as claimed in claim 6 wherein the height of said last cloverleaf section is approximately one-half the height of the normal cloverleaf sections.

11. An electron discharge device as claimed in claim 10 wherein the heights of the three sections preceding the last section, listed in order from the last section, are approximately /6, 5%, and 7; full height, respectively.

12. An electron discharge device comprising a cathode for producing a beam of electrons, a collector Ifor collecting said beam of electrons, a slow wave structure positioned between the cathode and collector for supporting a traveling wave, input means coupled to the cathode end of said slow-wave structure for introducing the traveling wave onto the slow-wave structure, the traveling wave being amplified by interaction with the electron beam traveling through the slow wave structure, said slow wave structure comprising a plurality of inductively coupled cloverleaf sections aligned along the beam path, the heights of the last several cloverleaf sections in the slow-wave structure decreasing in value progressively, the last cloverleaf section being substantially shorter in height than the full height of the normal cloverleaf sections, and output means coupled to said last cloverleaf section for removing the amplified wave from the slow-wave structure, said output means comprising a waveguide positioned between said last cloverleaf section and said collector, said output waveguide being coupled to said last section through a coupling hole in a wall separating said last section from said output waveguide, said coupling hole being coaxially aligned with the beam path through said slow-wave structure, said output waveguide having an annular capacitive tuning stub extending therein and aligned with the beam path and coupling hole for timing the output.

13. An electron discharge device comprising: means for directing an electron beam along an axial path; a slow wave structure having a plurality of inductively coupled cylindrical cloverleaf sections disposed axially between two points along said beam path; means for introducing a current density modulated beam to said cloverleaf sections at one such point; means for deriving an amplified output signal from said sections at the other of such points; at least one of the sections adjacent to such other point having a lesser height than the preceding adjacent section; said output signal deriving means including an output waveguide, and a capacitive tuning element penetrating said waveguide.

14. An electron discharge device comprising: a traveling wave portion having a plurality of inductively coupled cloverleaf sections disposed coaxially along a beam path; means for exciting a signal to produce a growing wave at said cloverleaf sections; means for deriving an amplified output signal from said cloverleaf sections, at least one of the sections at the end of such beam path having a lesser height than the preceding adjacent sections; said output signal deriving means including an output waveguide, and a capacitive tuning element penetrating said waveguide.

15. An electron discharge -device as in claim 14, further including a one-half wavelength dielectric window coupled to said waveguide.

16. An electron discharge device comprising: a traveling wave portion having first and second inductively coupled groups of cloverleaf sections disposed along a predetermined axis traversed by an electron beam in one direction; means for exciting a signal at said first group of such cloverleaf sections, each section of said first group having substantially the same height along such axis, said second group of cloverleaf sections having tapered heights progressively along said axis; means for deriving an output signal coupled to said second group of cloverleaf sections, said output signal deriving means including an output waveguide, and a capacitive tuning element extending into said waveguide aligned with said axis.

17. An electron discharge device comprising: a traveling wave portion including a multiplicity of cloverleaf parts in tandem, coaxially lined along a beam axis, said cloverleaf parts being negative mutually inductively coupled; means for inducing a signal at a first one of such multiplicity of said cloverleaf parts, said first one and a plurality of adjacent cloverleaf parts having substantially the same dimensions along the beam axis; ari output waveguide coupled to a last one of such multiplicity of cloverleaf parts by means of a central opening disposed concentrically with the beam axis, said last one and adjacent cloverleaf parts decreasing progressively in axial length in the direction of beam travel; and an annular capacitive tuning element penetrating such waveguide and aligned substantially with said beam axis.

18. An electron discharge device comprising: a traveling wave portion having a slow wave structure that includes a multiplicity of negative mutually inductively coupled cylindrical cloverleaf parts; means for inducing a signal of broadband frequency at said slow wave structure; an output circuit for deriving an amplified broadband signal fom said slow wave structure; a first group of' such cloverleaf parts having substantially the saine cylindrical height to achieve a constant phase velocity; a second group of such cloverleaf parts coupled between said first group and said output circuit, having progressively decreasing cylindrical heights to achieve a varying phase velocity; wherein said output circuit includes a waveguide shorted at one end and coupled to the last cloverleaf part of said second group; and a capacitive annular tuning element projecting into such waveguide.

References Cited UNITED STATES PATENTS 2,922,920 1/ 1960 Convert :H5-3.6 2,952,795 9/1960 Craig et al. 315-393 X 2,957,102 10/1960 Flannery et al. 3l5-3.5 3,289,032 1l/l966 Rubert et al. 315 3.6

HERMAN KARL SAALBACH, Primary Examiner. S. CHATMON, JR., Assistant Examiner. 

1. AN ELECTRON DISCHARGE DEVICE COMPRISING: A CATHODE FOR PRODUCING A BEAM OF ELECTRONS, A COLLECTOR FOR COLLECTING SAID BEAM OF ELECTRONS, A SLOW-WAVE STRUCTURE POSITIONED BETWEEN THE CATHODE AND COLLECTOR FOR SUPPORTING A TRAVELING WAVE, INPUT MEANS COUPLED TO THE CATHODE END OF SAID SLOW-WAVE STRUCTURE FOR INTRODUCING THE TRAVELING WAVE ONTO THE SLOW-WAVE STRUCTURE, THE TRAVELING WAVE BEING AMPLIFIED BY INTERACTION WITH THE ELECTRON BEAM TRAVELING THROUGH THE SLOW-WAVE STRUCTURE, SAID SLOW-WAVE STRUCTURE COMPRISING A PLURALITY OF INDUCTIVELY COUPLED CLOVERLEAF SECTIONS ALIGNED ALONG THE BEAM PATH, THE HEIGHTS OF THE LAST SEVERAL CLOVERLEAF SECTIONS IN THE SLOWWAVE STRUCTURE DECREASING IN VALUE PROGRESSIVELY, THE LAST CLOVERLEAF SECTION BEING SUBSTANTIALLY SHORTER IN HEIGHT THEN THE FULL HEIGHT OF THE NORMAL CLOVERLEAF SECTIONS, SAID INPUT MEANS INCLUDING A COAXIAL LINE EXTENDING INTO AND ACROSS THE FIRST CLOVERLEAF SECTION IN A DIRECTION PARALLEL TO THE BEAM PATH, SAID FIRST CLOVERLEAF SECTION HAVING AN ANNULAR TUNING STUB COAXIALLY ALIGNED WITH THE BEAM PATH AND EXTENDING INTO SAID FIRST CLOVERLEAF SECTION FOR CAPACITIVE TUNING OF THE INPUT, AND OUTPUT MEANS COUPLED TO SAID LAST CLOVERLEAF SECTION FOR REMOVING THE WAVE ENERGY FROM SAID SLOW-WAVE STRUCTURE. 